Project Summary/Abstract Over half of the world's children suffer from poor nutrition, and as a consequence they experience delays in physical and mental health, and cognitive development. Adverse environments, with limited access to stimulating settings and activities, unstable or crowded housing, and unsafe neighborhoods, also contribute to delays in growth and development. Despite evidence of the potential effectiveness of interventions in early childhood to promote growth and development, there is little evidence on the effectiveness of combined interventions operating at-scale, or on the sustainability of impacts. This study uses a multi-arm randomized-controlled trial (RCT) to test the cost-effectiveness of combined interventions to address chronic malnutrition and poor child development in Madagascar. The arms of the trial are: (T0) existing program with monthly growth monitoring and nutritional/hygiene education; (T1) T0 + home visits for intensive nutrition counseling within a behavior change framework; (T2) T1 + lipid-based supplementation (LNS) for children 6-18 months old; (T3) T2 + LNS supplementation of pregnant/lactating women; and (T4) T1 + intensive home visiting program to support child development. There are 25 communities in each trial arm (n=1250 pregnant women, n=1250 children 0-6 months old, and n=1250 children 6-12 months old). Primary outcomes include growth (length/height-for-age z-scores) and child development (mental, motor and social development and executive functioning). Secondary outcomes include caregiver reported child morbidity, household food security and diet diversity, maternal knowledge of child care and feeding and hygiene practices, quality of maternal-child interaction, and home stimulation practices. We will estimate unadjusted and adjusted intention-to-treat effects. This study builds on an existing multi-arm intervention trial in Madagascar. The proposed study includes analysis of data collected two years after program implementation began to estimate the impact of the different combinations of interventions. The study will build the evidence on the program effects and cost-effectiveness of different nutrition and child development strategies in varying combinations as preventive instruments in tackling long-term malnutrition and developmental delays. This study will be among the first to examine the relative effectiveness and cost- effectiveness of different packages on growth and child development outcomes in the context of a large-scale program.